Properties of low temperature sintered neodymium doped lead zirconate titanate ceramics

Abstract

The sintering of conventional PZT ceramics is highly energy intensive because the sintering is normally carried out at 1200-1300 °C. This gives rise to a number of processing difficulties such as the containment of PbO to maintain the stoichiometry. Therefore, the development of low sintering temperature piezoelectric ceramics will greatly reduce the energy consumption and the associated environmental pollution. This will also open up the possibility of using less expensive metals in multilayer piezoelectric devices [1-4]. Most of these investigations have found significant degradation of the properties. However, Zhilun et al. [1] have successfully used this glass frit without causing any adverse effect on the piezoelectric properties. The present work was undertaken to use this glass flit to reduce the sintering temperature of Pb(Zr,Ti)O3 ceramics to which varying quantities of Nd20 3 were added. A substantial enhancement of piezoelectric properties and grain refinement by neodymium addition has been observed [5]. Therefore, an attempt has been made to make use of the glass frit to bring about a reduction in sintering temperature of neodymium containing Pb(Zr,Ti)O3 ceramics without causing any adverse effect on their properties. The materials used for the present work were PbO, ZrO2, TiO2 and Nd20 3 having purity of 9 9 . 5 % . These materials were weighed corresponding to the composition Pb(Zr0.53Ti0.47)O3 + (0.00-5.00)mol% Nd20 3. A glass frit having composition 0.25BO1.5-0.5BiO1.5-0.25 CdO was melted and was mixed (5 wt %) with the basic PZT compositions. The PZT compositions containing flit (PZT-F) were sintered at 970 °C, resulting in a sintered density close to 95% of the theoretical density. The basic PZT compositions were, however, sintered at 1250 °C. All specimens were disc shaped; they were coated with fired-on silver paint and polarized at 130 °C using high d.c. electric field. The complete fabrication process is shown in Fig. 1. The dielectric constant (e') was measured using an HP-4192A LF impedance analyser at i kHz and electromechanical parameters were evaluated in accordance with the Institution of Radio Engineers specification [6]. The microstructural studies were performed on a Jeol JSM35CF scanning electron microscope (SEM). The addition of neodymium caused significant changes on almost all the dielectric and piezoelectric parameters, as shown in Table I. It can be seen from Table I that charge constant (d33) is highest for 2 mol % Nd 3+ content, and the corresponding values of the dielectric constant (e') and dielectric loss (tanr) are 960 and 0.008 respectively. Material with these values could be of immense importance if the sintering temperature could be brought down. Therefore, attention was focused on Pb(Zr0.53Ti0.47)O 3 + 2 mol % Nd20 3 composition. Fig. 2 shows the variation of density of PZT and PZT-F as a function of sintering temperature. The